Varicella Zoster Virus
Varicella zoster virus (VZV) causes two distinct clinical entities in humans: (a) chickenpox (varicella) and (b) herpes zoster or shin-gles. Chickenpox is acquired by transmission from an infected host to a susceptible host, whereas herpes zoster occurs as a result of reactivation of the latent virus. Contact with a case of zoster or chickenpox may transmit chickenpox but not herpes zoster.
Properties of the Virus
Varicella zoster virus (VZV) shows following features:
· The virus has the smallest genome of all the human herpesviruses.
· It is an enveloped, dsDNA virus showing many similarities with the HSV.
· The virus like that of the HSV encodes an enzyme thymidine kinase and is susceptible to antiviral drugs. It produces char-acteristic blister-like lesions and also has the ability to cause latent infections of nervous and recurrent disease. However, unlike HSV, VZV is transmitted mainly by the respiratory secretions.
· VZV shows a replicative cycle similar to that of HSV.
Virus Isolation and Animal Susceptibility
Varicella zoster virus grows readily in cultures of human fibro-blasts, human amnion, or HeLa cells. These cell cultures show an apoptotic effect similar to that seen in HSV-infected cells, but the lesions are less marked than those produced by HSV. Also, the CPE appears after a longer incubation period. In culture, the viruses remain associated with the cells and are not found free in the media. The virus does not grow in chick embryos or in experimental animals.